The present invention relates to an apertured web comprising a polymeric film having permanent hydrophilicity which is suitable for use as a topsheet in an absorbent article. The present invention also relates to absorbent articles incorporating a topsheet according to the present invention.
It has long been known in the field of disposable absorbent articles that it is extremely desirable to construct absorptive devices, such as disposable diapers, sanitary napkins, incontinent briefs, bandages, wound dressings, and the like, presenting a dry surface feel to the user to improve wearing comfort and to minimize the potential for development of undesirable skin conditions due to the prolonged exposure to moisture absorbed within the article. Accordingly, it is generally desirable to promote rapid fluid transfer in a direction away from the wearer and into a retentive structure, while resisting fluid transfer in the reverse direction.
One viable prior art solution to the aforementioned problem has been to utilize a covering or topsheet on the exposed, wearer-contacting layer which comprises a web of formed, apertured thermoplastic film. Commonly assigned US Patent 4,342,314, issued to Radel et al. on Aug. 3, 1982, the disclosure of which is hereby incorporated herein by reference, discloses a representative formed film of this variety. Such webs utilize capillary fluid transport to conduct fluid away from one surface (wearer-contacting) into and through the web via three-dimensional capillaries formed into the material, and then into the underlying absorbent structure. In order to address consumer concerns with regard to plastic-like appearance and feel, webs of this variety have been developed which include an interconnected structure of fiber-like appearance in the interest of generating a more cloth-like, aesthetically-pleasing appearance. In addition, apertured, formed thermoplastic film webs have been developed which further include microscopic surface texturing (microtexture) and/or microscopic apertures (microapertures) to further enhance the visual and tactile impression of such webs. Representative film webs of this variety are disclosed in commonly assigned U.S. Pat. No. 4,463,045, issued to Ahr et al. on Jul. 31, 1984, and U.S. Pat. No. 4,629,643, issued Dec. 16, 1986 to Curro et al., the disclosures of which are hereby incorporated herein by reference.
Another viable prior art solution has been to utilize a fibrous material as a covering or topsheet on such articles, alone or as an overlay or laminate over other materials. A representative topsheet structure of this variety is disclosed in Statutory Invention Registration H1670 published in the name of Aziz et al. on Jul. 1, 1997, the disclosure of which is hereby incorporated herein by reference. Such fibrous materials may take the form of a woven or nonwoven web of a suitable fiber variety, and may or may not include discretely formed apertures in addition to the inherent porosity of the web itself. Webs of this variety also exhibit capillary fluid transport characteristics via the three-dimensional capillaries formed by inter fiber spaces, likewise conducting fluid away from the wearer-contacting surface and into the underlying absorbent structure. Such webs exhibit an aesthetically-pleasing, cloth-like surface appearance and tactile impression due to the fibrous nature of the surface.
Another prior art solution to increase the rate of fluid transfer away from the wearer has been the addition of a surfactant, or wetting agent, to the web to increase wettability. The surfactant may either be incorporated into the web itself (resin incorporated surfactant (RIS)) in accordance with U.S. Pat. No. 4,535,020, issued in the name of Thomas, et al. on Aug. 13, 1985 and the aforementioned Statutory Invention Registration H1670, or, alternatively, may be applied to the surface of the web by spraying, printing, or other suitable methods such as disclosed in U.S. Pat. No. 4,950,264, issued to Osborn on Aug. 21, 1990.
The art has also used depositions of a low surface energy material on a surface of an apertured web having an underlying polymeric structure with a higher surface energy to provide a surface energy gradient. As described herein, such a surface energy gradient facilitates movement of moisture from the top surface of the web to the back surface. An example of this method is disclosed in commonly assigned U.S. Pat. No. 6,025,049, issued to to Ouelette et al. on Feb. 15, 2000. An exemplary coating material is a hydrophobic silicone resin. While such low surface energy depositions provide desirable fluid handling properties, they are relative expensive and require additional process steps.
While capillary webs of the foregoing varieties are effective in transporting fluid, their effectiveness is limited in that such capillary structures can only move fluid once it reaches the capillary interior. Fluid which wets and remains on wearer contacting surfaces contributes to a xe2x80x9cwetxe2x80x9d tactile feeling or impression, and to the extent that such fluid may be colored or opaque also contributes to a xe2x80x9cstainedxe2x80x9d visual impression. Surface textures naturally occurring in the material of the web or imparted thereto in formation further increase the likelihood that residual fluid will be trapped or retained on the wearer-contacting surface rather than entering capillary structures for transport away from the surface. Thus, surface topographies which contribute to desirable visual and tactile impressions when dry can also tend to retain residual fluid on the exposed surface and thus reduced desirability under in-use conditions.
Another problem associated with prior art capillary webs is their fluid retention when subjected to pressures associated with their use. The topsheet webs of the prior art do not prevent some of the fluid that has been transported away from the surface from passing back through the topsheet onto the wearer contact surface. As with fluid that remains on the wearer contact surface, fluid that passes back through the topsheet onto the wearer contact surface also contributes to a xe2x80x9cwetxe2x80x9d tactile feeling or impression, and a xe2x80x9cstainedxe2x80x9d visual impression.
Additionally, the RIS approach has several disadvantages. First, the surfactant is migratable, meaning that it may diffuse away from the topsheet, thus reducing topsheet wettability and possibly contaminating other components of the absorbent article. Second, surfactant may be lost during the forming process, thus potentially leading to foaming of the water system used for forming. Third, surfactant on the surface of the topsheet is normally depleted during use due to surfactant wash-off and migration. Finally, surfactants commonly used in absorbent articles are often complex molecules and mixtures of complex molecules. This results in surfactant having varying migration and therefore the topsheet experiences a surfactant composition that changes over time. The above disadvantages can result in a web having wettability with little durability.
Accordingly, it would be desirable to provide a web with enhanced effectiveness in transporting fluid away from one surface which is initially contacted by a fluid. It would also be desirable to provide a web that better prevents absorbed fluid from passing back out of the absorbent core of the article and onto the wearer contacting surface. Additionally, it would be desirable to provide a topsheet having durable wettability, i.e., permanent hydrophilicity, while avoiding the complexity of the RIS process. It would also be desirable to achieve a surface energy gradient while avoiding the use of hydrophobic coatings or surfactant treatments.
More particularly, it would be desirable to retain pleasing visual and tactile properties of webs having fibrous or otherwise textured surfaces while promoting more rapid and more complete fluid transport away from the wearer-contacting surface and into the interior of an associated absorbent article.
The present invention pertains to an apertured formed polymeric film web suitable for use as a topsheet on a disposable absorbent article. In one embodiment of the present invention the formed polymeric film web comprises a first layer, a second layer, and at least one intermediate layer between the first and second layers, where one of the first or second layers comprises a hydrophilic composition comprising a block copolymer of a polyether and another polymer, and the other layer comprises a hydrophobic composition as defined herein.
Another embodiment of the present invention is the formed polymeric film web comprises a first layer, a second layer, and at least one intermediate layer between the first and second layers, where both the first and second layers comprise a hydrophilic composition comprising a block copolymer of a polyether and another polymer.
A further embodiment of the present invention, the formed polymeric film web, comprises a dual-layer polymeric film comprising a first layer and a second layer where one of the first or second layers is hydrophilic and comprises a block copolymer of a polyether and another polymer and the other layer comprises a hydrophobic composition as defined herein.
A still further embodiment of the present invention the formed polymeric film web comprises a dual-layer polymeric film comprising a first layer and a second layer where both the first and second layers comprise a hydrophilic composition comprising a block copolymer of a polyether and another polymer.
A still further embodiment of the present invention the formed polymeric film web comprises a monolayer film comprising a hydrophilic layer comprising a block copolymer of a polyether and another polymer.
The polymeric film of the present invention provides many advantages. The use of a block copolymer of a polyether and another polymer as the hydrophilic layer renders the film permanently hydrophilic. The permanent hydrophilicity gives the film durable wettability without the need for surfactant treatment, thus avoiding the problems of the prior art.
The apertured formed film web, comprising a polymeric film in accordance with the present invention, may also be provided with a surface energy gradient, defined herein, which assist in the effective transport of fluid away from the first or wearer-contacting surface. The web essentially retains its visual, tactile, and physical properties of the substrate polymeric film material while achieving the desired surface energy properties.
The present invention also pertains to absorbent articles which preferably include a topsheet formed from the formed film web of the present invention, a backsheet secured to the topsheet, and an absorbent core positioned between the topsheet and the backsheet.